Impurity removal method of lithium sulfate slurry

Abstract

The invention provides an impurity removal method for lithium sulfate slurry, and relates to the technical field of lithium salt purification. The impurity removal method comprises the following steps: mixing lithium sulfate slurry with a reducing agent solution to form first to-be-reacted slurry; after the first to-be-reacted slurry is subjected to an oxidation-reduction reaction, a first mixture is obtained; mixing the first mixture with calcium carbonate to form a second slurry to be reacted; carrying out first precipitation on the second slurry to be reacted to obtain a second mixture; performing first solid-liquid separation on the second mixture to obtain a first liquid phase and a first precipitate; wherein the reducing agent comprises at least one of ferrous salt, sulfite and hydrosulfite, impurity elements can be removed to the maximum extent through the method, and the purity of the final product is improved.

Description

Technical Field

[0001] The present application belongs to the technical field of lithium salt purification, and specifically relates to a method for removing impurities from lithium sulfate slurry. Background Art

[0002] As one of the important strategic resources, lithium is widely used in many fields such as new energy vehicles, electronics, aerospace, etc. At present, lithium resources in lithium-containing ores are mainly extracted by sulfuric acid method. Taking spodumene as an example, in the traditional sulfuric acid method for producing lithium sulfate, the chemically stable α-type spodumene is first converted into β-type spodumene with high reactivity by high-temperature roasting. Then, the β-type spodumene is acidified and roasted with concentrated sulfuric acid at 250℃~330℃ to obtain an acidified material. In this reaction process, Li2O in β-type spodumene can be converted into soluble lithium sulfate. Finally, lithium sulfate slurry can be obtained by leaching the acidified material with water. Lithium sulfate slurry contains various impurity ions, such as Fe, Al, Cr, Si, Ca, Mg, etc. At present, the impurity ions are mainly removed by adding alkaline substances to precipitate them. However, due to the oxidation reaction of lithium ore during high-temperature roasting, Cr exists mainly in the form of Cr(VI) in the lithium sulfate slurry. The traditional impurity removal process cannot effectively precipitate Cr(VI), and the impurity ions in the lithium sulfate slurry are high, resulting in the product failing to meet quality requirements. Summary of the invention

[0003] The main purpose of the present application is to provide a method for removing impurities from lithium sulfate slurry to solve the problem that chromium element is difficult to remove from lithium sulfate slurry in the prior art.

[0004] In order to achieve the above object, the present application provides, on the one hand, a method for removing impurities from lithium sulfate slurry, comprising the following steps:

[0005] S1, mixing lithium sulfate slurry and reducing agent solution to form a first slurry to be reacted; the first slurry to be reacted undergoes an oxidation-reduction reaction to obtain a first mixed material;

[0006] S2, mixing the first mixed material with calcium carbonate to form a second slurry to be reacted; subjecting the second slurry to be reacted to a first precipitation to obtain a second mixed material; subjecting the second mixed material to a first solid-liquid separation to obtain a first liquid phase and a first precipitate;

[0007] Wherein, the reducing agent includes at least one of ferrous salt, sulfite and bisulfite.

[0008] Furthermore, the method further comprises the following steps:

[0009] S3, mixing the first liquid phase, sodium hydroxide solution and sodium carbonate solution to form a third slurry to be reacted; subjecting the third slurry to be reacted to a second precipitation to obtain a third mixed material; subjecting the third mixed material to a second solid-liquid separation to obtain a refined lithium sulfate liquid and a second precipitate.

[0010] Furthermore, the reducing agent includes at least one of ferrous sulfate, sodium sulfite, and sodium bisulfite.

[0011] Further, the pH value of the second mixed material is 4.5-5.0; and / or,

[0012] The pH value of the third mixture is 9-12.

[0013] Furthermore, the volume mass ratio of the reducing agent solution to the lithium sulfate slurry is 1L:(200L-2000L), and the density of the lithium sulfate slurry is 1.1kg / m 3 ~1.3kg / m 3 , the mass concentration of the reducing agent solution is 100g / L to 500g / L; and / or,

[0014] The volume mass ratio of the first mixed material to calcium carbonate is 1L: (60g-120g).

[0015] Furthermore, the volume ratio of the first liquid phase to the sodium hydroxide solution is 100:(0.2-2.0),

[0016] The mass concentration of the sodium hydroxide solution is 40% to 60%; and / or, the amount of the sodium carbonate solution added is 2 to 10 times the volume of the first liquid phase; and / or,

[0017] The concentration of the sodium carbonate solution is 250 g / L to 350 g / L.

[0018] Furthermore, the temperature of the redox reaction is 25° C. to 60° C., and the time of the redox reaction is 1 h to 6 h.

[0019] Further, the temperature of the first precipitation is 25° C. to 60° C., and the time of the first precipitation is 1 h to 6 h; and / or,

[0020] The temperature of the second precipitation is 60° C. to 90° C., and the time of the second precipitation is 1 h to 4 h.

[0021] Furthermore, S1 includes: mixing a reducing agent with water to obtain a reducing agent solution; mixing lithium sulfate slurry with the reducing agent solution to form a first slurry to be reacted; and obtaining a first mixed material after the first slurry to be reacted undergoes an oxidation-reduction reaction.

[0022] Furthermore, the pH value of the lithium sulfate slurry is 0.5 to 2.5.

[0023] Furthermore, the concentration of Li2O in the lithium sulfate slurry is 20g / L~25g / L, the concentration of Na element is 1.1g / L~1.5g / L, the concentration of Fe element is 2g / L~3g / L, the concentration of Al element is 2g / L~3g / L, the concentration of Si element is 32mg / L~53mg / L, the concentration of Cr element is 6.8mg / L~11.05mg / L, the concentration of Ca element is 0.5g / L~0.6g / L, and the concentration of Mg element is 0.5g / L~0.6g / L.

[0024] By applying the technical solution of the present application, at least one of ferrous salt, sulfite and bisulfite is used as a reducing agent, Cr(VI) in lithium sulfate slurry can be reduced to Cr(III), thereby effectively removing it in the subsequent impurity removal step, solving the problem that chromium is difficult to remove in lithium sulfate slurry in the prior art. This method can not only improve the removal efficiency of chromium, but also maintain efficient removal of other impurities (such as iron, aluminum, silicon, calcium, magnesium, etc.) without introducing additional impurities, thereby improving the purity of the final product and having significant industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 This is a process flow chart of a method for removing impurities from lithium sulfate slurry in one embodiment of the present application;

[0027] Figure 2 The distribution of stable species of Cr(III) in different pH ranges at 40℃;

[0028] Figure 3 The distribution of stable species of Cr(III) in different pH ranges at 90℃;

[0029] Figure 4 The stable species distribution of Cr(VI) in different pH ranges at 40℃;

[0030] Figure 5 The distribution of stable species of Cr(VI) in different pH ranges at 90℃;

[0031] Figure 6 The distribution of stable species of Fe(II) in different pH ranges at 40℃;

[0032] Figure 7The stable species distribution of Fe(III) in different pH ranges at 40℃. DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below in conjunction with the embodiments.

[0034] As described in the background technology, the existing lithium sulfate slurry has the problem that chromium is difficult to remove. In order to solve the above technical problems, Figure 1 As shown, the present application provides a method for removing impurities from lithium sulfate slurry, comprising the following steps:

[0035] S1, mixing lithium sulfate slurry with a reducing agent solution to form a first slurry to be reacted; the first slurry to be reacted undergoes an oxidation-reduction reaction to obtain a first mixed material;

[0036] S2, mixing the first mixed material with calcium carbonate to form a second slurry to be reacted; subjecting the second slurry to be reacted to a first precipitation to obtain a second mixed material; subjecting the second mixed material to a first solid-liquid separation to obtain a first liquid phase and a first precipitate;

[0037] Wherein, the reducing agent includes at least one of ferrous salt, sulfite and bisulfite.

[0038] In step S1, lithium sulfate slurry is mixed with a reducing agent solution to perform a redox reaction. The reducing agent reduces Cr(VI) in the lithium sulfate slurry to Cr(III). Specifically, when the reducing agent is a ferrous salt, the following reaction occurs: 3Fe 2+ +Cr 6+ =Cr 3+ +3Fe 3+ , where both Fe(II) and Fe(III) can be precipitated and removed in the subsequent reaction; when the reducing agent is sulfite, the following redox reaction occurs: 3SO3 2- +2Cr 6+ =2Cr 3+ +3SO4 2- When the reducing agent is bisulfite, the following redox reaction occurs: 3HSO3 - +2Cr 6+ =2Cr 3+ +3SO4 2- +3H + , of which SO4 2 - Lithium sulfate slurry already exists, so no new impurities are significantly introduced. When sulfite is in excess, it is easily oxidized to SO4 2-, which also reduces the impact on the purity of the final lithium sulfate product. In short, compared with other reducing agents, the present application uses at least one of ferrous salts, sulfites, and bisulfites as a reducing agent to reduce hexavalent chromium in lithium sulfate slurry, which can reduce hexavalent chromium that is difficult to precipitate and remove to trivalent chromium that is easy to precipitate and remove without introducing additional impurities.

[0039] In step S2, the first mixture is mixed with calcium carbonate (CaCO3), and calcium carbonate as a neutralizer can adjust the pH value of the solution to a suitable weakly acidic or neutral range, so that metal ions such as Cr(III), Fe(II), Al(III), and Si(IV) react with calcium carbonate to form a water-insoluble precipitate to obtain a second mixture. After the second mixture is separated by the first solid-liquid separation, a first liquid phase and a first precipitate are obtained, wherein Cr(III), Fe(II), Al(III), and Si(IV) in the first liquid phase have been removed, and the first precipitate contains precipitates formed by metal ions such as Cr(III), Fe(II), Al(III), and Si(IV).

[0040] The present application uses a suitable reducing agent to convert Cr(VI) into Cr(III), which is easier to handle, and combines it with graded precipitation to effectively remove multiple impurities (Fe, Al, Cr, Si, Ca, Mg) in the lithium sulfate slurry. This method can not only improve the purity of lithium sulfate, but also reduce production costs and environmental impact. The selection of reducing agents avoids the introduction of additional impurities and improves the quality of lithium sulfate products.

[0041] In some embodiments, the following steps are also included: S3, mixing the first liquid phase, sodium hydroxide solution and sodium carbonate solution to form a third slurry to be reacted, and obtaining a third mixed material after the third slurry to be reacted undergoes a second precipitation; performing a second solid-liquid separation on the third mixed material to obtain a refined lithium sulfate liquid and a second precipitate.

[0042] In step S3, the first liquid phase is mixed with a sodium hydroxide (NaOH) solution and a sodium carbonate (Na2CO3) solution to further increase the pH value of the solution and to react the Ca(II) in the first liquid phase with the CO3 2- CaCO3 precipitates are formed, Fe(III), Mg(II) and OH - Mg(OH)2 precipitate is formed to obtain a third mixed material. The third mixed material is separated by a second solid-liquid separation to obtain a lithium sulfate refined liquid with higher purity and a second precipitate, wherein the second precipitate contains precipitates formed by Ca(II), Mg(II) and Fe(III).

[0043] It should be noted that the Ca(II) in the first liquid phase includes the Ca(II) originally present in the lithium sulfate slurry, and also includes the Ca(II) remaining after the first precipitation of the calcium carbonate introduced in S2. These Ca(II) are precipitated and removed together through S3.

[0044] In some embodiments, the first solid-liquid separation and the second solid-liquid separation can be achieved by using a plate and frame filter press.

[0045] In some embodiments, the reducing agent includes at least one of ferrous sulfate, sodium sulfite, and sodium bisulfite. These reducing agents can reduce Cr(VI) present in the lithium sulfate slurry to Cr(III), so that Cr(III) can be effectively removed by a subsequent precipitation step. In addition, Fe(III) generated during the reduction of ferrous sulfate can be removed by subsequent further precipitation, while SO4 2 - is already present in the lithium sulfate slurry, so no new impurities are introduced significantly. SO4 generated after the reaction of sodium sulfite and sodium bisulfite 2 - is already present in the lithium sulfate slurry, so no new impurities will be significantly introduced. In addition, sulfite is easily oxidized to sulfate in the case of excess, which also reduces the impact on the purity of the final lithium sulfate product.

[0046] By using one or a combination of the above reducing agents, the Cr(VI) content in the lithium sulfate slurry can be more effectively reduced, and a purer lithium sulfate solution can be obtained through subsequent precipitation and solid-liquid separation steps. This process not only improves the quality of the final product, but also minimizes potential harm to the environment.

[0047] In some embodiments, the pH value of the second mixture is 4.5 to 5.0. By controlling the pH value of the second mixture, it can also be understood that the pH value of the first precipitation reaction endpoint is controlled to be 4.5 to 5.0, which can optimize the precipitation process, improve the removal efficiency of Cr(III), Fe(II), Al(III), and Si(IV), and avoid the use of excessive precipitants, thereby reducing costs.

[0048] In some embodiments, the pH value of the third mixture is 9 to 12. By controlling the pH value of the third mixture, it can also be understood that the pH value of the reaction endpoint of the second precipitation is controlled to be 9 to 12, which can optimize the precipitation process, improve the removal efficiency of Ca (II), Mg (II), and Fe (III), and avoid the use of excessive precipitants, thereby reducing costs.

[0049] In some embodiments, the volume ratio of the reducing agent solution to the lithium sulfate slurry is 1 L: (200 L to 2000 L) and the density of the lithium sulfate slurry is 1.1 kg / m 3 ~1.3kg / m3 , the mass concentration of the reducing agent solution is 100g / L~500g / L. By reasonably controlling the dosage of the reducing agent, the best Cr(VI) removal effect can be achieved while minimizing the impact on the removal process of other impurities.

[0050] In some embodiments, the volume mass ratio of the first mixture to calcium carbonate is 1L:(20g-40g), for example 1L:20g, 1L:25g, 1L:30g, 1L:35g, 1L:40g or a range consisting of any two of them.

[0051] In the specific implementation process of the present application, calcium carbonate can be first mixed with water to form a slurry, and then the first mixture can be mixed with the slurry. The fineness of calcium carbonate in the slurry is usually high, which can increase its dispersibility in the solution, making the reaction more uniform and thorough. Among them, the volume ratio of the first mixture to the slurry is 1L: (0.05L~0.1L), for example, 1L: 0.05L, 1L: 0.08L, 1L: 0.1L or a range consisting of any two of them; the mass concentration of calcium carbonate in the slurry is 400g / L~600g / L, for example, 400g / L, 450g / L, 500g / L, 550g / L, 600g / L or a range consisting of any two of them.

[0052] In some embodiments, the volume ratio of the first liquid phase to the sodium hydroxide solution is 100:(0.2-2), for example, 100:0.2, 100:0.5, 100:1, 100:2, or a range consisting of any two of them. The mass concentration of the sodium hydroxide solution is 40-60%, for example, 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of them. In some embodiments, the volume ratio of the first liquid phase to the sodium carbonate solution is 1:(2-10), for example, 1:2, 1:4, 1:6, 1:8, or a range consisting of any two of them. The concentration of the sodium hydroxide solution is 250g / L-350g / L, for example, 250g / L, 295g / L, 305g / L, 350g / L, or a range consisting of any two of them. By controlling the amount of sodium hydroxide solution and sodium carbonate added, Ca(II) and Mg(II) can be removed to the maximum extent.

[0053] In some embodiments, the temperature of the redox reaction is 25° C. to 60° C., and the time is 1 hour to 6 hours. Within this temperature and time range, the redox reaction can be fully carried out, effectively reducing the valence state of the chromium ions, facilitating subsequent precipitation removal, while avoiding the increase in energy consumption that may be caused by high temperature and long reaction time.

[0054] In some embodiments, the temperature of the first precipitation is 25° C. to 60° C., and the time is 1 h to 6 h. Within this temperature and time range, the first precipitation can be fully carried out, so that Cr(III), Fe(II), Al(III), and Si(IV) can be removed more effectively.

[0055] In some embodiments, the second precipitation temperature is 60° C. to 90° C., and the time is 1 h to 4 h. This reaction condition optimizes the precipitation process, so that Ca(II), Mg(II), and Fe(III) can be removed more effectively, while ensuring the recovery rate of lithium ions.

[0056] In the specific implementation process of the present application, S1 includes: mixing a reducing agent with water to obtain a reducing agent solution; mixing lithium sulfate slurry with the reducing agent solution to form a first slurry to be reacted; and the first slurry to be reacted undergoes an oxidation-reduction reaction to obtain a first mixed material. By first mixing the reducing agent with water, it is helpful to disperse them evenly and achieve sufficient oxidation-reduction reaction.

[0057] The lithium sulfate slurry can be prepared by mixing the acidified material with water. The density of the lithium sulfate slurry is 1.1 kg / m 3 ~1.3kg / m 3 , for example 1.1kg / m 3 , 1.15kg / m 3 , 1.2kg / m 3 , 1.25kg / m 3 , 1.3kg / m 3 The mass concentration of the reducing agent solution is 100 g / L to 500 g / L, for example, 100 g / L, 200 g / L, 300 g / L, 400 g / L, 500 g / L or a range consisting of any two thereof.

[0058] The lithium sulfate slurry of the present application can be obtained by sequentially subjecting lithium-containing ore to high-temperature roasting, acid roasting, and water leaching, and the lithium sulfate slurry contains various impurity ions, such as Fe, Al, Cr, Si, Ca, Mg, etc. The present application does not limit the specific type of lithium sulfate slurry. For example, in some embodiments, the pH value of the lithium sulfate slurry is 0.5 to 2.5, such as 0.5, 1, 1.5, 2, 2.5, or a range consisting of any two of them.

[0059] In some embodiments, the concentration of Li2O in the lithium sulfate slurry is 20g / L to 25g / L, the concentration of the Na element is 1.1g / L to 1.5g / L, the concentration of the Fe element is 2g / L to 3g / L, the concentration of the Al element is 2g / L to 3g / L, the concentration of the Si element is 32mg / L to 53mg / L, the concentration of the Cr element is 6.8mg / L to 11.05mg / L, the concentration of the Ca element is 0.5g / L to 0.6g / L, and the concentration of the Mg element is 0.5g / L to 0.6g / L. Through the method provided in this application, the lithium content can be significantly increased, the content of Fe, Al, Si, Cr, Ca, and Mg elements can be reduced, and the utilization efficiency of lithium resources can be effectively improved.

[0060] The lithium sulfate refined liquid finally obtained in the present application contains high-purity lithium sulfate and can be directly used in the production of lithium battery materials.

[0061] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0062] Example 1

[0063] The density of the lithium sulfate slurry in this embodiment is 1.2 kg / m 3 , pH value is 1, of which Li2O concentration is 20g / L, Na element concentration is 1.2g / L, Fe element concentration is 2g / L, Al element concentration is 3g / L, Si element concentration is 53mg / L, Cr element concentration is 6.8mg / L, Ca element concentration is 0.5g / L, and Mg element concentration is 0.5g / L.

[0064] The impurity removal method of lithium sulfate slurry in this embodiment comprises the following steps:

[0065] S1, adding 0.25 mL of ferrous sulfate solution with a concentration of 200 g / L to 500 mL of lithium sulfate slurry, reacting at a temperature of 25° C. for 3 hours to perform an oxidation-reduction reaction to obtain a first mixed material;

[0066] S2, mixing the first mixed material with limestone slurry (mass concentration of 500 g / L), reacting at 50° C. for 6 hours, controlling the pH value of the reaction end point to be 4.6, to obtain a second mixed material; performing solid-liquid separation on the second mixed material through a plate and frame filter press to obtain a first liquid phase and a first precipitate;

[0067] S3, reacting the first liquid phase, sodium hydroxide solution and 4 times the volume of sodium carbonate solution (compared to the volume of the first liquid phase) at 80°C for 4 hours, controlling the pH value of the reaction end point to be 12.0, to obtain a third mixture; passing the third mixture through a plate and frame filter press for solid-liquid separation to obtain a refined lithium sulfate liquid and a second precipitate; wherein the added volume of the sodium hydroxide solution is 0.4% of the volume of the first liquid phase, the mass concentration of the sodium hydroxide solution is 50%, and the concentration of the sodium carbonate solution is 300 g / L.

[0068] Example 2

[0069] The density of the lithium sulfate slurry in this embodiment is 1.28 kg / m 3 , pH value ≤ 1, where Li2O concentration is 25g / L, Na element concentration is 1.4g / L, Fe element concentration is 3g / L, Al element concentration is 3g / L, Si element concentration is 44mg / L, Cr element concentration is 11.05mg / L, Ca element concentration is 0.6g / L, and Mg element concentration is 0.6g / L.

[0070] The impurity removal method of lithium sulfate slurry in this embodiment comprises the following steps:

[0071] S1, adding 1.25 mL of ferrous sulfate solution with a concentration of 200 g / L to 500 mL of lithium sulfate slurry, reacting at a temperature of 50° C. for 5 hours to perform an oxidation-reduction reaction to obtain a first mixed material;

[0072] S2, mixing the first mixed material with limestone slurry (mass concentration of 500 g / L), reacting at 50° C. for 5 hours, controlling the pH value of the reaction end point to be 4.8, to obtain a second mixed material; performing solid-liquid separation on the second mixed material through a plate and frame filter press to obtain a first liquid phase and a first precipitate;

[0073] S3, reacting the first liquid phase, sodium hydroxide solution and 6 times the volume of sodium carbonate solution (compared to the volume of the first liquid phase) at 90°C for 2h, controlling the pH value of the reaction end point to be 10.0, to obtain a third mixture; passing the third mixture through a plate and frame filter press for solid-liquid separation to obtain a refined lithium sulfate liquid and a second precipitate; wherein the added volume of the sodium hydroxide solution is 0.6% of the volume of the first liquid phase, the mass concentration of the sodium hydroxide solution is 50%, and the concentration of the sodium carbonate solution is 295g / L.

[0074] Example 3

[0075] The density of the lithium sulfate slurry in this embodiment is 1.30 kg / m 3, pH value ≤ 1, where Li2O concentration is 22g / L, Na element concentration is 1.1g / L, Fe element concentration is 2g / L, Al element concentration is 3g / L, Si element concentration is 48mg / L, Cr element concentration is 7.53mg / L, Ca element concentration is 0.5g / L, and Mg element concentration is 0.6g / L.

[0076] The impurity removal method of lithium sulfate slurry in this embodiment comprises the following steps:

[0077] S1, adding 2.5 mL of ferrous sulfate solution with a concentration of 200 g / L to 500 mL of lithium sulfate slurry, reacting at a temperature of 60° C. for 4 hours to perform an oxidation-reduction reaction to obtain a first mixed material;

[0078] S2, mixing the first mixture with limestone slurry (mass concentration of 500 g / L), reacting at 60° C. for 4 hours, controlling the pH value of the reaction end point to be 4.7, to obtain a second mixture; performing solid-liquid separation on the second mixture by a plate and frame filter press to obtain a first liquid phase and a first precipitate;

[0079] S3, reacting the first liquid phase, sodium hydroxide solution and 8 times the volume of sodium carbonate solution (compared to the volume of the first liquid phase) at 70°C for 3h, controlling the pH value of the reaction end point to be 9.0, to obtain a third mixture; passing the third mixture through a plate and frame filter press for solid-liquid separation to obtain a refined lithium sulfate liquid and a second precipitate; wherein the added volume of the sodium hydroxide solution is 0.8% of the volume of the first liquid phase, the mass concentration of the sodium hydroxide solution is 50%, and the concentration of the sodium carbonate solution is 305g / L.

[0080] Example 4

[0081] The density of the lithium sulfate slurry in this embodiment is 1.25-1.30 kg / m 3 , pH value ≤ 1, where Li2O concentration is 22g / L, Na element concentration is 1.5g / L, Fe element concentration is 3g / L, Al element concentration is 2g / L, Si element concentration is 32mg / L, Cr element concentration is 10.03mg / L, Ca element concentration is 0.6g / L, and Mg element concentration is 0.5g / L.

[0082] The impurity removal method of lithium sulfate slurry in this embodiment comprises the following steps:

[0083] S1, adding 2.5 mL of ferrous sulfate solution with a concentration of 200 g / L to 500 mL of lithium sulfate slurry, reacting at a temperature of 40° C. for 4 hours to perform an oxidation-reduction reaction to obtain a first mixed material;

[0084] S2, mixing the first mixed material with limestone slurry (mass concentration of 500 g / L), reacting at 40° C. for 4 hours, controlling the end point pH value of the reaction to be 4.75, to obtain a second mixed material; performing solid-liquid separation on the second mixed material through a plate and frame filter press to obtain a first liquid phase and a first precipitate;

[0085] S3, reacting the first liquid phase, sodium hydroxide solution and 10 times the volume of sodium carbonate solution (compared to the volume of the first liquid phase) at 90°C for 2h, controlling the pH value of the reaction end point to be 11.0, to obtain a third mixture; passing the third mixture through a plate and frame filter press for solid-liquid separation to obtain a refined lithium sulfate liquid and a second precipitate; wherein the added volume of the sodium hydroxide solution is 0.6% of the volume of the first liquid phase, the mass concentration of the sodium hydroxide solution is 50%, and the concentration of the sodium carbonate solution is 300g / L.

[0086] Example 5

[0087] The difference from Example 1 is that in S1, 2.5 mL of ferrous sulfate solution with a concentration of 200 g / L is replaced by 2.5 mL of sodium sulfite solution with a concentration of 200 g / L.

[0088] Example 6

[0089] The difference from Example 1 is that in S1, 2.5 mL of ferrous sulfate solution with a concentration of 200 g / L is replaced by 2.5 mL of sodium bisulfite solution with a concentration of 200 g / L.

[0090] Example 7

[0091] The difference from Example 1 is that in S2, the pH value at the reaction end point is controlled to be 4.5.

[0092] Example 8

[0093] The difference from Example 1 is that in S2, the pH value at the reaction endpoint is controlled to be 5.0.

[0094] Example 9

[0095] The difference from Example 1 is that in S2, the pH value at the reaction endpoint is controlled to be 2.5.

[0096] Example 10

[0097] The difference from Example 1 is that in S3, the pH value at the reaction endpoint is controlled to be 3.0.

[0098] Comparative Example 1

[0099] The difference from Example 1 is that S1 is omitted.

[0100] Comparative Example 2

[0101] The difference from the first embodiment is that S1 and S2 are omitted.

[0102] Comparative Example 3

[0103] The difference from the first embodiment is that S1 and S3 are omitted.

[0104] The lithium sulfate refined liquid finally formed in the embodiment and the comparative example was tested for the content of Cr, Al, Fe, Si, Ca and Mg by ICP-OES, and the detection limit was 0-15 mg / L. It should be noted that the content of Cr in the lithium sulfate refined liquid was ≤0.2 ppm, which was qualified.

[0105] The test results are shown in Table 1.

[0106] Table 1

[0107]

[0108] Figure 2 and Figure 3 The stable species distribution of Cr(III) in different pH ranges at 40℃ and 90℃ respectively. Figure 4 and Figure 5 The stable species distribution of Cr(VI) in different pH ranges at 40℃ and 90℃ respectively.

[0109] according to Figure 2 and Figure 3 It can be seen that when pH>5, Cr(III) exists in the form of CrO(OH) precipitation. Figure 4 and Figure 5 It can be seen that in SO4 2- In the system, Cr(VI) does not precipitate when the pH value is between 0 and 14. Therefore, for Cr(VI), it is impossible to precipitate and remove Cr(VI) in the solution by adjusting the pH. The present application reduces Cr(VI) to Cr(III) by introducing a reducing agent, so that it can be precipitated and removed in the subsequent steps.

[0110] Figure 6 and Figure 7 The stable species distribution of Fe(II) and Fe(III) in different pH ranges at 40℃ are shown respectively. Figure 6 and Figure 7 It can be seen that Fe(II) and Fe(III) are precipitated and removed in the primary impurity removal section of S2 and the secondary impurity removal section of S2 respectively. Fe(II) is removed in the form of Fe(OH)2 precipitation when pH>8, and Fe(III) is removed in the form of Fe(OH)3 precipitation when pH>3. 2+ It does not affect the precipitation and impurity removal effect of iron ions with different valence states during the impurity removal process.

[0111] According to Table 1, the embodiment of the present application utilizes at least one of ferrous salt, sulfite and bisulfite as a reducing agent, which can reduce Cr(VI) in the lithium sulfate slurry to Cr(III), thereby effectively removing it in the subsequent impurity removal step, significantly improving the removal efficiency of the chromium element, and maintaining efficient removal of other impurities (such as iron, aluminum, silicon, calcium, magnesium, etc.) without introducing additional impurities, thereby improving the purity of the final product and having significant industrial application potential.

[0112] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those described herein, for example.

[0113] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for removing impurities from lithium sulfate slurry, characterized in that: The following steps are involved: S1, mixing the lithium sulfate slurry with a reducing agent solution to form a first slurry to be reacted; the first slurry to be reacted undergoes an oxidation-reduction reaction to obtain a first mixed material; S2, mixing the first mixed material with calcium carbonate to form a second slurry to be reacted; subjecting the second slurry to be reacted to a first precipitation to obtain a second mixed material; subjecting the second mixed material to a first solid-liquid separation to obtain a first liquid phase and a first precipitate; Wherein, the reducing agent in the reducing agent solution includes at least one of ferrous salt, sulfite and bisulfite.

2. The impurity removal method according to claim 1, characterized in that: The following steps are also included: S3, mixing the first liquid phase, sodium hydroxide solution and sodium carbonate solution to form a third slurry to be reacted, and obtaining a third mixed material after the third slurry to be reacted undergoes a second precipitation; and performing a second solid-liquid separation on the third mixed material to obtain a refined lithium sulfate liquid and a second precipitate.

3. The impurity removal method according to claim 1, characterized in that: The reducing agent includes at least one of ferrous sulfate, sodium sulfite and sodium bisulfite.

4. The impurity removal method according to claim 1, characterized in that: The pH value of the second mixture is 4.5 to 5.0; and / or, The pH value of the third mixed material is 9-12.

5. The impurity removal method according to any one of claims 1 to 3, characterized in that: The volume ratio of the reducing agent solution to the lithium sulfate slurry is 1L: (200L~2000L), the density of the lithium sulfate slurry is 1.1kg / m 3 ~1.3kg / m 3 , the mass concentration of the reducing agent solution is 100 g / L to 500 g / L; and / or, The volume mass ratio of the first mixed material to the calcium carbonate is 1L: (60g~120g).

6. The impurity removal method according to any one of claims 1 to 3, characterized in that: The volume ratio of the first liquid phase to the sodium hydroxide solution is 100: (0.2～2.0)， The mass concentration of the sodium hydroxide solution is 40% to 60%; and / or, The volume of the sodium carbonate solution is 2 to 10 times the volume of the first liquid phase; and / or, The concentration of the sodium carbonate solution is 250 g / L to 350 g / L.

7. The impurity removal method according to any one of claims 1 to 3, characterized in that: The temperature of the oxidation-reduction reaction is 25° C. to 60° C., and the time of the oxidation-reduction reaction is 1 h to 6 h; and / or, The temperature of the first precipitation is 25° C. to 60° C., and the time of the first precipitation is 1 h to 6 h; and / or, The temperature of the second precipitation is 60° C. to 90° C., and the time of the second precipitation is 1 h to 4 h.

8. The impurity removal method according to any one of claims 1 to 3, characterized in that: S1 includes: The reducing agent is mixed with the water to obtain a reducing agent solution; the lithium sulfate slurry is mixed with the reducing agent solution to form the first slurry to be reacted; and the first slurry to be reacted is subjected to the oxidation-reduction reaction to obtain the first mixed material.

9. The impurity removal method according to any one of claims 1 to 3, characterized in that: The pH value of the lithium sulfate slurry is 0.5-2.

5.

10. The impurity removal method according to any one of claims 1 to 3, characterized in that: The concentration of Li2O in the lithium sulfate slurry is 20g / L-25g / L, the concentration of Na element is 1.1g / L-1.5g / L, the concentration of Fe element is 2g / L-3g / L, the concentration of Al element is 2g / L-3g / L, the concentration of Si element is 32mg / L-53mg / L, the concentration of Cr element is 6.8mg / L-11.05mg / L, the concentration of Ca element is 0.5g / L-0.6g / L, and the concentration of Mg element is 0.5g / L-0.6g / L.

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